Woman arrested after body of newborn found in bin

The woman believed to be the mother of a newborn baby found dead in a bin last month has been arrested.

The boy was found naked inside a rubbish bag in an apartment block bin on Harrow Road at Auburn on August 31 by a local resident.

NSW police put out a desperate plea to find the baby's mother, saying their main priority was getting her medical care.

More than three weeks later, police said a 24-year-old woman believed to be the infant's mother had been identified.

She was taken to hospital for assessment and then arrested upon her release on Thursday evening and taken to Auburn Police Station.

The woman remains in custody and is expected to be charged, police said.

Auburn Police Area Acting Commander Darren Sly said it was believed the baby had been in the bin for up to 36 hours.

"It's sad and a horrific set of circumstances," he told reporters on the day the boy was found.